The invention relates to a blade for a fluid-flow or turbo machine being directed along a blade axis and having a root end region, a tip end region and a center region disposed therebetween along the blade axis, and a cross-sectional region at right angles to the blade axis. The invention also relates to a steam turbine, in particular a high-pressure or intermediate-pressure steam turbine.
The efficiency of a fluid-flow machine, in particular of a steam turbine, is reduced by flow losses which occur. An improvement in the efficiency and thus also a reduction of such flow losses is dealt with, for example, in an article entitled xe2x80x9cAdvanced Steam Turbine Technology for Improved Operating Efficiencyxe2x80x9d by R. B. Scarlin, in xe2x80x9cPower-Gen Europe 95xe2x80x9d, May 16-18, 1995, Amsterdam RAI, the Netherlands, Book 2, Vol. 4, page 229 ff. The development of three-dimensional turbine blades with regard to various flow losses, such as gap losses, losses due to the blade profile, and losses in the end regions of the turbine blade (end wall losses), is described in that article. An inclination of the turbine blade in the circumferential direction is specified in order to reduce the last-mentioned losses. An inclination of the turbine blade in the region of the blade tip as well as in a hub region of the turbine blade leads to a bent blade, in which case such a bend, due to the mechanical properties, can only be used in guide blades. Furthermore, it is stated globally in the article that twisting of the blade also has an effect on the inclination of the blade, so that the blade inclination, the blade twist as well as the blade profile are available in a three-dimensional structure in the end regions of the blade.
European Patent Application EP 0 704 602 A2, corresponding to U.S. Pat. No. 5,779,443, concerns the structure of a turbine guide blade in an intermediate stator of a steam turbine directed along a turbine axis. The blade in that case extends along a radially directed blade axis and has a pressure side and a suction side as well as an inlet edge and an outlet edge. In that case the blade is shaped along the radial direction in such a way that the pressure side has a convex curvature from a blade root region to a blade tip region lying opposite the blade root region along the blade axis.
In a particularly preferred structure, the curvature is achieved by a setting angle (bitangential angle) on radially successive, cross-sectional profiles at a distance from one another being varied parabolically with respect to the turbine axis by an appropriate rotation of the cross-sectional profiles about a fixed common outlet edge. In this way, the channel width for the steam can be reduced in the blade tip region and in the blade root region and can be increased in a blade center region lying therebetween. That leads to a shifting of part of the steam mass flow, away from the two loss-affected marginal regions of the turbine guide blade.
An increase in the efficiency of a steam turbine, in particular of a high-pressure or intermediate-pressure steam turbine, is likewise dealt with in an article entitled xe2x80x9cModern Blade Design for Improving Steam Turbine Efficiencyxe2x80x9d by M. Jansen and W. Ulm in xe2x80x9cVDI Berichtexe2x80x9d No. 1185, 1995, pages 277-290. The effect of various flow losses for various steam turbines is explained therein. A reduction in the flow losses is achieved by a special configuration of the turbine blade. In that case, the three-dimensionally constructed turbine blades have an inclination in a root region and a tip region of the turbine blade. In the article, a comparison is made between the flow losses of those three-dimensionally constructed turbine blades and entirely cylindrical blades.
Such cylindrical blades have pressure and suction sides parallel to the blade axis and therefore have neither a twist nor an inclination. So-called twisted turbine blades, which have an increasing twist and a changing blade profile over their height, are described as a further alternative to the three-dimensionally constructed turbine blades.
German Published, Non-Prosecuted Patent Application DE 31 48 995 A1 describes an axial-flow turbine, such as a steam turbine or a gas turbine, with a multiplicity of guide blades disposed at a distance from one another along the circumference. The guide blades being used are twisted over their height and have a changing inlet angle. The changing of the inlet angle increases continuously in an overlinear manner in the region of the tip of the guide blade, as from a certain height measured from the blade root. The twisting likewise increases continuously over the height of the guide blade. The cross-sectional profile of the guide blade changes continuously from the blade root to the blade tip, with the guide blade becoming increasingly slender. Further changes concerning the outlet angle, the size and the shape of the guide blade are taken into account over the height of the guide blade in the shaping of the guide blade.
German Published, Prosecuted Patent Application 1 168 599 specifies an axial-flow compressor with moving blades and/or guide blades, which have a cross-section that is changed in the region of wall surfaces to compensate for an influence on the flow brought about by those wall surfaces. In the axial-flow compressor, inlet guide blades are disposed along the gas flow path upstream of the moving blades and guide blades. Those inlet guide blades have a convex cross-section, other than in the region of the walls. A middle part of the blade, with the convex cross-section, changes over in each wall region into the un-convex cross-sectional profile in the wall regions in a smooth and constantly curved surface. The cross-sectional profiles of the blade aerofoil consequently change continuously over the height of the inlet guide blade. The inlet angle remains constant over the entire height of the inlet guide blade.
German Published, Prosecuted Patent Application 28 41 616 contains a description of a guide blade rim for an axial-flow turbine with guide blades. The guide blades are disposed between an inner ring and an outer ring and the profile thickness of the blade aerofoil changes proportionally to the blade pitch. In that case the changing of the blade profile over the height of the guide blade does not take place by a change occurring in the shape of the leading edge (pressure side), but instead the projection on the trailing edge gradually increases in size over the height, with a simultaneous increase in the thickness of the guide blade.
The changing of the profile is carried out in that case by an increase in the thickness of the guide blade, while its chord length remains the same. A guide blade rim of that kind can be used in the case of steam turbines, gas turbines and compressors.
German Published, Non-Prosecuted Patent Application DE 42 28 879 A1 specifies an axial-flow turbine having at least one row of curved guide blades. The blade curvature has the effect that both the inlet edge and the outlet edge of the guide blades do not lie in one and the same axial plane. The curvature of the blades in that case runs at right angles to the chord, which is achieved by a displacement of the profile sections both in the circumferential direction and in the axial direction. The guide blades taper from a turbine casing wall (cylinder) to a turbine hub, so that their cross-section changes correspondingly, with the blade profile remaining essentially unchanged over the height of the blade. Apart from the curvature and the tapering, a twisting of the blade aerofoil is also carried out over the blade length of the guide blade, in order to allow for the changing of the circumferential speed of the moving blades following the guide blade over the channel height. Consequently, an adaptation of the blade aerofoil takes place by a deflection of the center of gravity of the profile sections at right angles to the profile chord (curvature or bending), that is to say a simultaneous axial deflection and circumferential deflection, combined with a variation in the chord length.
Turbine blades provided with an inclination for a steam turbine are likewise specified in an article entitled xe2x80x9cDevelopment of three-dimensional stage viscous time marching method for optimization of short height stagesxe2x80x9d by G. Singh, P. J. Walker and B. R. Haller, in xe2x80x9cVDI-Berichtexe2x80x9d No. 1185, 1995, pages 157-179.
It is accordingly an object of the invention to provide a blade for a fluid-flow machine, and a steam turbine, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which have low flow losses.
With the foregoing and other objects in view there is provided, in accordance with the invention, a fluid-flow machine blade directed along a blade axis, comprising a root end region; a tip end region disposed opposite the root end region along the blade axis; a center region disposed between the root end region and the tip end region; a cross-sectional profile at right angles to the blade axis; cross-sectional profiles disposed at a distance from one another axially in direction of the blade axis and offset from one another by a translation in a given cross-sectional direction in the tip end region towards the center region; cross-sectional profiles disposed at a distance from one another axially and offset from one another by a translation in the given cross-sectional direction in the root end region towards the center region; and cross-sectional profiles disposed at a distance from one another axially and twisted relative to one another by a respective differential angle in the root end region and/or in the tip end region.
When a blade is fitted in a turbine having a turbine shaft, the term axially in the direction of the blade axis is synonymous with the term radially relative to the turbine shaft. A reduction in the flow losses in the marginal zones (tip end region, root end region), which are assigned to the hub of a turbine shaft and to the inner periphery of a turbine casing, is achieved by cross-sectional profiles disposed at a distance from one another axially being displaced in the tip end region and in the root end region and by an additional twist in the root end region and/or in the tip end region. The equidirectional displacement towards the center region causes the turbine blade to be inclined (bent) in a bulged manner at right angles to the blade axis. An additional increase in the efficiency, i.e. a reduction in the flow losses, is achieved by an additional twist of the cross-sectional profiles at a distance from one another axially.
In accordance with another feature of the invention, the cross-sectional regions at a distance from one another axially are twisted equidirectionally in the root end region and in the tip end region towards the center region. In this way, the twist is withdrawn again across the entire height of the blade from the tip end region towards the root end region.
In accordance with a further feature of the invention, the blade is constructed for placement in a blade rim which has a circumferential direction, and the cross-sectional direction coincides locally with the circumferential direction. In this way, a bend in the circumferential direction with a simultaneous twist (angular adaptation) in the end regions of the blade is effected in the marginal zones of the blade, as a result of which a reduction in the flow losses and thus an increase in the efficiency of a fluid-flow machine can be achieved. As a result, in particular in steam turbines, an increase in the mechanical output energy with the same thermal energy input is achieved on one hand, and a reduction in the thermal energy input and thus in the environmental pollution due to pollutant discharge, while the output energy remains the same, is achieved on the other hand, as compared with entirely cylindrical or entirely inclined or entirely bent blades.
In accordance with an added feature of the invention, the cross-sectional profiles, during twisting, are twisted relative to their area center of gravity or relative to the blade axis (if different, e.g. due to inhomogeneous mass distribution). The angle of twist which occurs in the process is designated below as a xe2x80x9cstagger anglexe2x80x9d and execution of the twist is designated as a xe2x80x9cstagger-angle changexe2x80x9d.
In accordance with an additional feature of the invention, in a cross-section at right angles to the blade axis, the cross-sectional profile is identical everywhere along the blade axis. The cross-sectional profile therefore does not change over the height of the blade. In this case, the cross-sectional surface of the cross-sectional profile is also preferably constant. In this case, the blade preferably has a combination of a circumferential deflection of the center of gravity of the cross-sectional profiles (bending in the circumferential direction) and a staggering of the cross-sectional profiles (without changing of the profiling) in the tip end region and root end region (hub region and casing region).
In accordance with yet another feature of the invention, depending on the extent of the blade in the direction of the blade axis (blade length, blade height) relative to the extent of the blade in a direction at right angles to the blade axis (blade width) and on the flow conditions during the use of the blade in a fluid-flow machine, the blade has a cylindrical structure in the center region. The sides (pressure side, suction side) of the blade therefore run parallel to the blade axis.
In accordance with yet a further feature of the invention, the blade is constructed as a guide blade or a moving blade of a steam turbine, in particular of a high-pressure or intermediate-pressure steam turbine. In this case, the blade preferably has a small length-to-width ratio, as is the case in particular in blades for a high-pressure steam turbine.
With the objects of the invention in view there is also provided a steam turbine, in particular a high-pressure or intermediate-pressure steam turbine directed along a turbine axis, comprising an inflow region; an outflow region; a blading region disposed fluidically between the inflow region and the outflow region; and a blade directed along a blade axis and disposed in the blading region, the blade having a root end region, a tip end region, a center region between the end regions, and an inclination and a twist over the blade axis, the inclination and the twist each increasing from the root end region to the center region and decreasing from the center region to the tip end region. With such a configuration of the steam turbine, including the blade with decreasing and increasing inclination and twist, a reduction in the flow losses in the region of a turbine shaft directed along the turbine axis and in the region of a turbine casing surrounding the turbine shaft is achieved.
In accordance with another feature of the invention, the blade with decreasing and increasing inclination and twist is assigned to the inflow region. It is therefore preferably disposed in the first stage and/or the following stages. This applies to stages including a blade rim being formed of moving blades or guide blades. Since, in the first stages of a high-pressure or intermediate-pressure steam turbine, the proportion of so-called secondary losses (marginal losses) in the hub and casing regions is especially high (e.g. up to 30% of the total losses) and is reduced by the blade shape specified, a noticeable increase in the efficiency can thereby be achieved.
In accordance with a further feature of the invention, a twisted blade, i.e. a blade having a twist and change of the cross-sectional profile and/or the cross-sectional surface which increases over its length, is assigned to the outflow region.
In accordance with a concomitant feature of the invention, an entirely cylindrical blade, i.e. having side walls parallel to the blade axis, is provided axially between the stages including the twisted blade and the blade with decreasing and increasing inclination and stagger-angle change. Such a configuration of blades of different geometry provides for a steam turbine which has low flow losses and has high efficiency.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a blade for a fluid-flow machine, and a steam turbine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.